Being unrestricted, scientific theories cannot be verified by any
possible accumulation of observational evidence. The formation of
hypothesis is a creative process of the imagination and is not a passive
reaction to observed regularities. A scientific test consists in a
persevering search for negative, falsifying instances. If a hypothesis
survives continuing and serious attempts to falsify it, then it has
``proved its mettle'' and can be provisionally accepted, but it can
never be established conclusively. Later corroboration generates a
series of hypothesis into a scientific theory.

Thus, the core element of a scientific hypothesis is that it must be
capability of being proven false. For example, the hypothesis that
``atoms move because they are pushed by small, invisible, immaterial demons'' is pseudo-science since the existence of the demons cannot be proven
false (i.e. cannot be tested at all).